Pulverization system



Feb. 6, 1940.. M. FRISCH PULVERIZA TION SYSTEM Originl Filed March so,1932 2 Sheets-Sheet 1 INVENTOR" 4 H| x. Y

VIII/1142717?!) M M ATTORNEY Feb. 6, 1940. M. FRISCH 'PULVER'IZATIONSYSTEM Original Filed March 30, 1932 2 Sheets-Sheet 2 INVENTOR PatentedFeb. 6, 1940 PATENT OFFICE PULVERIZATION SYSTEM Martin Frisch, New York,N. Y., assignor 'toFoster Wheeler Corporation, New York, N. Y.,acorporation of New York Application March 30, 1932, Serial No. 601,917Renewed April 23, 1938 v 9 Claims.

My invention relates to apparatus for and method of pulverizing materialand more particularly for pulverizing coal. My invention involves anovel combination of pulverizing apparatus and classifying apparatus.

The principal object of my invention is to provide an improved method ofsweeping a pulverizingmill and particularly a ball type mill with airand returning partially pulverized material to the mill for furthertreatment.

Another object of. my invention is to increase the amount of partiallypulverized material entering the classifier, thus increasing the localcirculation of coal out of and back into the mill.

16 Increasing the amount of material to be circulated increases thepulveiizing capacity of the mill.

A still further object is to mix moist incoming material withrecirculated oversize material 20 which hasalready been partially driedby its passage through the pulverizer. The oversize will absorb moisturefrom the fresh wet-material by contact and thus serve to distribute anddilute the moisture so that the average moisture content 25 of thematerial delivered to the. grinding elements is reduced. The capacity ofa pulverizer is greater when fed with dry material than when fed withmoist material. Hence the power consumption per unit of materialpulverized will be lower.

80 In ball mills of the conical type, material being pulverized tends totake different positions along the axis of the mill depending upon itssize. The coarser particles take a position toward the charging or inletend of the mill while the finer 85 particles gather at the apex of thecone-shaped portion. As the material is pulverized it automaticallytravels from the inlet to the apex of the cone. Heretofore it has beenthe practice to sweep a ball mill with a current of air entering 40 thecoal charging end leaving at the coal discharge end. In the presentinvention the current of air used to sweep the mill leaves the mill atthe coal charging end. Since the direction of the current of air throughthe mill is counter-current 45 to the general direction of movement ofmaterial pulverized, more partially finished product will be drawn fromthe mill than was formerly the practice. Additionally, a greater dryingof the material undergoing pulverization is effected because 50 the hightemperature air first comes in contact with the high temperaturematerial in the drum.

A classifier is located adjacent the material inlet end 01' the mill.Material to be pulverized. which may be raw coal containing aconsiderable amount of moisture, is fed through the classifier in such amanner that partially pulverized material, hereafter referred to asoversize, is mixed therewith before entering the mill. This has theeffect of drying the raw coal pr other material and making it easier topulverize, thereby reduc- 5 ing the power consumption per unit materialpulverized. p

The greater the amount of oversize recirculated the greater will be thecapacity of the mill. This result follows from the fact that ma- 10terial undergoing pulverization in a ball mill consists of a large masscontaining'fine particles of material which require no furthertreatment, and a considerable portion of oversize which is notcommercially usable. Very fine and very coarse coal may be foundthroughout the ball mass. But the finer material eventually gathers atthe small end of the conical shell remote from the feed trunnion. Eventhough the quality of the product desired from a pulverizer is usuallydescribed by stating the amount that will pass a screen of a given size,for example a screen of 200 meshes to the inch, it is possible for apulverizer to deliver product of the required quality with a greaterexpenditure of work than necessary and hence at the expense ofpulverizer capacity and with a greater power consumption. This followsfrom the factthat the material passing the 200 mesh screen is made up ofa mixture of particles containing varying numbers per unit weight .whichare all smaller than the aperture of a 200 mesh screen. Since the workdone by a pulverizer per unit weight of material depends on the increasecaused in the number of particles per unit weight of materialpulverized, it follows that the greater the number of fine particlesproduced the smaller will be the output of a pulverizer, and the greaterthe power consumption. Consequently, the maximum capacity will beobtained from a pulverizer when the ratio of the number of new particlesproduced to the desired percentage through the required screen size is aminimum. It is obvious therefore that if particles are withdrawn fromthe pulverizer as soon as they are of the proper size to avoidover-pulveri zation, the pulverizer capacity will be at a maximum. Thiscondition is best approached by withdrawing to a classifier materialfrom the pulverizer at a rate greater than the desired capacity so thatin the classifier the coarse ma- 5 terial may be separated from thefinished product and returned to that portion of the grinding zone wheremost of the coarse material is to be found. To that end the air sweepingthe mill is made to pick up a relatively great amount of oversize whichis mostly carried into the classifier, some being dropped at once in thevicinity of the large grinding balls which are pulverizing relativelycoarse material. Oversize is returned from the classifier to the regionof coarse material in the rotating drum. This oversize is more quicklypulverized when mixed with coarser particles than when allowed to remainwhere it naturally segregates. Thus the fines are removed as soon as.possible and the oversize is subject to vigorous treatment at once.Another factor which also increases the capacity of the mill is thatwith a large portion of circulating oversize, that is, circulationbetween classifier and mill, the classifier is actingas a part of millproper since in effect, it extends the volumetric capacity of the ,Agreat deal of heat is generated in the mill when material is pulverized.The oversize absorbs some of this heat and heat thus absorbed is used todryraw material entering the classifier. It is of advantage then toplace the classifier as close as possible tothe milland to increase theamount of oversize withdrawn, in order to obtain the most beneficial useof the heat carried out of the mill by the oversize.

- Other features and advantages of my invention will become apparentfrom the following detailed description of certain approved embodimentsthereof, of which:

Fig. 1 is a vertical; longitudinal sectional view through the mill andclassifier as arranged for a unit system; v

Fig. 2 is a transverse sectional view of the classifier taken on line2-2 of Fig.- 1;

Fig. 3 is a view similar to Fig. 1 but showing a storage system; a

Fig. 4 is a transverse sectional view of a modifled form of classifiertaken on line 4-4 of Fig. 3

Fig. 5 is a section taken on line 5-5 of Fig. 4 showing the arrangementof a pair of screw conveyors; and

Fig. 6 shows a vertical cross-sectional view of a modified form ofclassifier having a double spiral passage instead of a single spiralpassage as in Fig. 2.

Referring now to Fig. 1, It represents a ball mill of the conical type.Hollow trunnions l1 and -'shell is mounted to rotate about a horizontalThe classifier I8 is provided with a conduit connection l9 which extendsinto the hollow trunnion l2 of the ball mill. Between the end walls 20and 2| of the classifier is a spirally curved member 22 which togetherwith the partitioii 23 and the walls 24 and 24' provides a spirallyshaped passage 25. The inlet to the passage 25 is' the conduitconnection 19 while the outlet conduit is shown at26. The partition 23and wall 21 provide a chute 28 for feeding material to be pulverized bythe mill. A check damper 29 extends across and controls the flow area ofthe'chute '28. A chamber 30 is provided for receiving'oversize. Acontrol damper 82 is hinged to the end of curved member 22. A controldamper 83 is provided in the passageway 25. A by-passvalve or damper 84is provided to permit passage of fluid through member 22 without passingthrough passage 25. These various dampers'may be suitably provided withshaft extensions passing through the classifier casing and nion openingII by supports 41.

- 32 of the screw conveyor A is the pulley 33, which through a belt andpulley 34 rotates the rotor of the air lock 38. I

The screw conveyor A extends into, and throughout the length of theconduit connection It of the classifier. A spider 35 fixed to therotating steel shell rotates the horizontal shaft 32 of the conveyor.The central portion of the screw 36 is open to permit ready passage ofair therethrough. 1

Access doors 3| are provided in the wall of the classifier in suitablepositions.

A horizontal screw conveyor B extends into the opposite trunnion openingII. A shaft 31, to which screw 33 is attached, is rotated by a spider 33connected to the steel shell. The screw 38 is formed so as to causegrinding balls or solid particles passing into trunnion I l to becarried back through the trunnion into the mill. The screw 38 is twistedin a direction opposite to screw 38, so that both conveyors will feedtoward the center of the mill as the steel shell is rotated.

An exhaust fan 4|! having its inlet connected to conduit 26 beyond theclassifier and driven by an electric motor 4| serves to draw a currentof air, which mayor may not be preheated, through the mill from conduit42. In conduit 42 a series of dampers 33 control flow of air into thehollow trunnion II. The damper 44 serves as an additional means forcutting oil. the air sup- -.ply.through conduit 42. Preheated oratmospheric air. as desired, may enter through conduit 42. A damper 45'serves totemper the preheated air with atmospheric air and also to varythe amount of air drawn into the mill. A manually adjustable damper 46is shown in conduit 26.

Conduit 42 is suitably supported in the trun- The classifier issupoprted by supports 48.

- Theoperation of the arrangement shown by Fig. 1 is as follows:

Let it be assumed that the pulverizing unit is to be used for supplyingpulverized coal directly to a burner. Coal which has been crushed to asuitable "size enters the mill through passage 28 arranged on the sideof the classifier iii. A damper 29 operates to control the passage ofcoal to the screw conveyor A rotated by the spider 35 fixed to the steelshell of the mill. Coal is carried into the mill by the screw conveyor Aand is pulverized by the grinding balls and by attrition between thecoal particles which are cascaded over each other by the rotation of thesteel shell. The shell or drum l5 may be rotated through ring gear I! bymeans of a suitably mounted pinion gear driven in any desired manner' asfrom an electric motor. New grinding balls may be fed to the millthrough the slide door 45. The screw conveyor driven through spider 39is adapted to carry the new balls into the mill. The screw conveyorJBacts to prevent coal and grinding balls from obstructing the trunnionopening Ii.

The fan 40 driven by motor ll operates to sweep the mill with a currentof air. Air entering the mill through conduit 42 is directed downwardlyand varied in amount by dampers 43. The damper 44 may be used to cut offthe air supply in 'a single movement when desired. The air enteringconduit 42 may be atmospheric or preheated. An opening controlled bydamper 45' serves to temper'preheated air by mixing atmospheric airtherewith, and also serves as a means for admitting additional air.

The dampers 43, 44, 45', and 46 which are manually adjustable, determinethe amount and character of air to be used in sweeping the mill. Thequantity and velocity of the current of air passing through the milldetermines the fineness or grade of material carried out of the mill.The greater the quantity and the higher the rate of flow, the greaterthe proportion of large particles of coal removed from the mill. Openingdamper 46 at the inlet to the fan and partially closing damper 44 withdamper 45' completely closed effects a slowing up of the rate of fiowand a lessening of the quantity of material withdrawn. This operationcauses only very fine coal dust to be removed with a minimum of coarseparticles or oversize. An operation which permits fines to remain in themill after having ben reduced to a usable state requires a great deal ofadditional power per unit material pulverized. The fan is preferablydriven at constant speed to maintain a constant uninterrupted fiowthrough the discharge conduit to the burner.

In practice,-the present invention permits the use of large quantitiesof air at a high rate of flow with the view to reducing, the powerconsumption per unit of coal pulverized to a minimum. This is broughtabout by the location and use of classifier l8. As indicated onthedrawings, the classifier is of large size and is preferably of avolume at least as great as'one quarter the volume of the rotatabledrum. Air carrying a heavy cloud of coal dust leaves the mill throughthe central open portion of conveyor A and enters the spiral passage 25,and thence passes through fan 46 to use. The oversize separated out ofthe moving cloud of dust, due to the change of direction in theclassifier and preferably expansion of the area of fiow, is collected inchamber 36 and passes through the rotating valve 3| to conveyor A.Oversize and raw coal are mixed by the conveyor before entry to 'themill. This mixing causes heat from the oversize to dry the raw coalsomewhat. As is well known, 'coal having a high moisture contentrequires as much as 20% more power for pulverization. It is desirable toreduce the moisture content as much as possible in order to reduce thepower consumption.

The operation of the classifier can be readily controlled by members 62,83 and 84.

A modified form of classifier is shown in the arrangement according toFig. 3. The function and operation of the classifier in this figure isthe same as in Fig. 1. The arrangement of mill and classifier is verywell adapted for use in what has become known as a "storage system asdistinguished from the system shown in Fig. 1 in which the pulverizedmaterial leaving the exhaust fan goes directly to use.

Elements in Fig 3 which correspond to like ele-'- In the trough-likebottom 5| of the classifierv are two screw conveyors 52 and 53. 54 is amotor and reduction gearing. v The conveyors are driven by motor 54through belt 55 and gears 56 and 51. Since the screw conveyors rotate inopposite directions the screw on one conveyor is opposite to the other.This causes material to be thrown to the center of the trough and forcedthrough the inlet trunnion opening.

Conduit 26 leads to a dust separator 58 of the cyclone type which iswell known in the art to which this application pertains. At the bottomof the separator is a rotatable valve or air lock 59 through whichcollected material passes to storage bin 60. This air lock may likewisecomprise a continuously rotating member including axial vanes.

Between the cyclone separator and fan 46 is a therein similar to valve59. A manually controlled damper 69 is located in the vent 63. The

. air return conduit is connected to the conduit 42 through which airreenters the mill.

The operation of the mill and classifierin Fig. 3 is similar to Fig. 1.The fan 46 is located beyond the cyclone separator 58 and draws the coaldust laden air from the classifier thereto. Pulverized coal thusseparated out drops to the bottom of the separator 58 and passes throughvalve 59 to storage bin 66 from which place it is used as desired. Theopening in conduit 6| regulated by adjusting slide 62 varies thevelocity and quantity of air pulled through the mill in much the samemanner as damper 46. Damper 44 and the opening varied by slide 45 havethe same function as the elements having like reference 'characters inFig. 1.

Because of the fact that some air leaks into a system such as shown inFig. 3, or preheated air may be purposely introduced and mixed with thereturn air in order to accelerate the drying of the coal during thepulverizing process, a vent 63 must be provided for the discharge of theexcess air. A portion of the air which is returnedby the fan to theinlet end of the mill escapes around the damper 69 to conduit 63 andinto chamber 65. From chamber 65 the air flows through the fiat screensor bags 66 to the atmosphere through outlet 61. The coal dust thuscollected passes through the valve conduit to storage bin 66.

In the modified form of classifier shown in Fig. 6,. the stream of airand pulverized material in passage .10 is divided at a central pointintermediate the axes c and d of the classifier, This gives what may betermed a double spiral fiow for passage of air carrying pulverizedmaterial and'is adapted to materially increase the capacity of theclassifier. The guide walls H and 12 together with the casing 13 providetwo'spiral passages 14 and I5. Oversize which drops out at thetermination of these passages is caused to pass through air looks orvalves 16 and 11 which may be rotated from the shaft .18 of the screwconveyor 19 in the same manner as indicated in Fig. 1. The oversizeismixed with raw coal entering the conveyor 19 .and is conveyed to themill. Control and by-pass valve or'damper members may be provided as inthe embodiment. of

, Fig. 1.

While mylnvention' has been described in connection with a ball mill ofthe conical type, it will be understood that its application is notspecifically limited thereto, but may be employed with other types ofmills, and it is to be further understood that I do not limit myself toany particular embodiment except as defined in the appended claims.

Having thus described my invention, what I claim is:

1. In an apparatus for pulverizing material, a rotatable shell havinghollow trunnions, pulverizing means in the shell, a classifier having aninlet connection extending into one of the trunnions, a conveyorarrangedin said inlet connection for moving material into the shell, a conveyorextending into the other trunnion for preventing passage of materialtherethrough, said conveyors being connected to be driven from therotatable shell, and suction means connected to causea current of air tofiow in through said other trunnion and out through the first mentionedtrunnion for carrying pulverized material from the shell to theclassifier.

2. In an apparatus for pulverizing material, a rotatable shell havinghollow trunnions, pulverizing means in the shell, a classifier having aninlet connection extending into one of the trunnions, a conveyorarranged in said inlet connection for moving material into the shell, aconveyor extending into the other trunnion for preventing passage ofmaterial therethrough, said conveyors being connected to be driven fromthe rotatable shell, suction means connected to cause a current of airto fiow in through said other trunnion and out through the firstmentioned trunnion for carrying pulverized material from the mill to theclassifier, and means for controlling the flow of air.

3. A feeder and classifier for pulverization apparatus comprising innerand outer members forming a spiral passage and a supply passage,

a conveyor in the lower part thereof in communication with the supplypassage, a pocket above the conveyor and in communication with thespiral passage, and means to conduct material from said pocket to saidconveyor.

4. A feeder and classifier for pulverization apparatus comprising innerand outer members forming a spiral passage and a supply passage, aconveyor in the lower part thereof in communication with the supplypassage, a pocket above the conveyor and in communication with thespiral passage, and an air lock between said pocket and said conveyor.

5. A feeder and classifier for pulverization apparatus comprising acurved passage and a sup ply passage separate from each other, aconveyor in communication with the supply passage, a pocket incommunication with the curved passage, means to conduct material fromthe pocket to the conveyor, and a passage connecting the initial andterminal portions of the curved passages.

6. A'feeder and classifier for pulverization apparatus comprising acurved passage and a supair to fiow through the shell for carryingpulverized material from the shell, and a conduit between the shell andthe suction means, a unitary feeder and classifier comprising a spiralpassage and a supply passage separate from each other, the spiralpassage having one end connected with one of said trunnions and theother end connected with said conduit so that air is drawn through saidone trunnion and the spiral passage, a movable conveyor at the dischargeend of the supply passage, a pocket in communication with the spiralpassage, and means to conduct material from the pocket to the conveyor.

8. In pulverization apparatus including a shell having hollow trunnions,pulverizing means in the shell, suction means for causing a current ofair to flow through the shell for carrying pulverized material from theshell, and a conduit between the shell and the suction means, a unitaryfeeder and classifier comprising a spiral passage and a supply passageseparate from each other, the spiral passage having one end connectedwith one of said trimnions and the other end connected with said conduitso that air is drawn through said one trunnion and the spiral passage, amovable conveyor at the discharge end of the supply passage, a pocket incommunication with the spiral passage, and an air lock between thepocket and the conveyor.

9. In pulverization apparatus including a shell having hollow trunnions,pulverizing means in the shell, suction means for causing a current ofair to flow through the shell for carrying pulverized material from theshell, and a conduit between the shell and the suction means, aclassifier-comprising a plurality of separate spiral passages, eachspiral passage'having one end connected with one of said trunnions andthe other end connected with said conduit so that air is drawn throughsaid one trunnion and each of the spiral passages, a movable-conveyor atthe lower portion of the classifier, a pocket in communication with eachof the spiral passages, and means for conducting material from thepockets to the movable conveyor.

' MARTIN FRISCH.

